#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>

int main()
{
    long n = 0;
    scanf("%d", &n);
    long long sum = 0;
    while (n > 0)
    {

        sum = sum + n;
        n = n - 1;
    }
    printf("%lld", sum);








    return 0;
}